Redox flow batteries (RFB) have attracted considerable research interests primarily due to their ability to store large amounts of power and energy, up to multi-MW and multi-MWh, respectively. RFB systems are considered one of the most promising technologies to be utilized not only for renewable energy resources integration, but also to improve the efficiency of grid transmission and distribution. With the energy supplied from externally stored electrolytes, the dissociation of energy capacity and power capability offers unique design latitude for RFBs to be sized for a wide spectrum of power and energy storage applications. Other advantages of RFBs include high safety, quick response, long service life, deep discharge ability, etc.
Due to limits of the water electrolysis potential window and the solubility of the active materials in water, traditional aqueous RFBs are typically considered to be low energy density systems (<25 Wh/L in most true flow battery systems). While significant progress has been made to improve the energy density, aqueous RFB systems can still be severely hindered by the poor solubility and stability of the active materials in the solutions. In this regard, a non-aqueous energy storage system that utilizes at least some aspects of RFB systems is attractive because it offers the expansion of the operating potential window, which can have a direct impact on the system energy and power densities.